Introduction to Acoustics
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Transcript of Introduction to Acoustics
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Introduction to Acoustics
dr inż. Michał [email protected]
Visitng hours:
tuesday 15:00-16:00
wednesday 10:00-11:00
„Lodex” 207
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Acoustics[gr. akoustikós ‘related to hearing’]
field of physics and engineering that deals with the study of all mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound
http://www.physics.byu.edu/2
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Sound
„phys. mechanical disturbance in a compressive medium capable of inducing an auditory sensation, as well as the auditory sensation itself” (Encyklopedia PWN)
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Longitudinal wave (wzdłużna)
Particles oscillate in the direction of wave propagation.
Areas of increased and decreased pressure.
http://www.physics.byu.edu/
What’s the range of movement of the air particles moved by sound?
0.008nm to 0.1 mm
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Harmonic signal
http://hyperphysics.phy-astr.gsu.edu
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Physics vs. perception
Physical definitions:
- Intensity (natężenie) or
amplitude (amplituda)
- Frequency (częstotliwość)
- Spectrum (widmo)
- Speed (prędkość)
Psychoacustic definitions:
- Loudness (głośność)
- Pitch/tone (wysokość/ton)
- Tembre (barwa)
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Speed of soundc = 344 m/s
c = 331 + 0,6*T[oC]gestosc
sztywnoscCc
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Intensity of soundIntensity = the amount of energy passing through an area in time
224 m
W
r
PI
http://hyperphysics.phy-astr.gsu.edu
How does amplitude change with distance?
22 ~~~ ApEP
rrIA
1~
1~~
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Measures of sound level
Pressure (rms)
from 0.00002 N/m2 (threshold of hearing)
to 20 N/m (threshold of pain)
atmospheric pressure
100000 N/m2
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Decibel scaleRatio of power:
Ratio of amplitude:
dB power ratio amplitude ratio
60 1 000 000 1 000
50 100 000 316.2
40 10 000 100
30 1 000 31.62
20 100 10
10 10 3.162
6 3.98 2
3 2 1.414
0 1 1
-3 0.5 0.7071
-6 0.251 0.5
-10 0.1 0.3162
-20 0.01 0.1
-30 0.001 0.03162
-40 0.000 1 0.01
0
110log10P
PLdB
20
21
10log10A
ALdB
0
110log20A
ALdB
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Confusing „sound levels”Sound Power Level (SWL)
- energy emitted by sound source per second (cause)
Sound Pressure Level (SPL)
- pressure (amplitude) changes at receiver (effect)
Sound Intensity Level (SIL)
- energy delivered to receiver area per second (effect)
μPa200 p 212
0 mW10P
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http://www.physics.byu.edu/
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Loudness1Fon = 1dBSPL at 1kHz
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Frequency
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Audio frequency ranges
Tones Examples
Low bass: 20 – 80 Hz
Lowest two octaves. Explosions, storms, lowest church organ notes
Upper bass: 80 – 320 Hz
3th – 4th octavesDrums, bass, cellos, wind instruments
Lower mid: 320 – 2560 Hz
5th – 7th octavesMost instruments and human speech
Upper mid: 2560 – 5120 Hz
8th octaveHighest notes on most instruments, whistles, most sensitive perception range
High/treble: 5120 Hz – 20000 Hz
9th -10th octavePercussion (hi-hat, cymbal), higher harmonics of sounds, noise
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Human perception
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Musical tone (pitch)
Musical scales
– divided into octaves (intervals), e.g. C (dur)
A4 = 440Hz
Psychoacoustic scales
– Mel or Barkhttp://www.sfu.ca/
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Freq. components
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Fourier transform
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Spectrum of a sound
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Real spectrumA
mpl
itud
a (d
B)
Częstotliwość (Hz)
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Cutting the spectrum into octaves
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Tembre/qualitySet of features distinguishing sounds of the same base frequency on different instruments
Spectrum dependent (harmonics and noise) and transients (sudden changes)
Described semantically (np.brightness, warmth, coarsness, clarity)
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Sound envelope
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Anatomy of hearing
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Cochlea
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Future topics - Psychoacoustics- Spatial audio- Room acoustics (wave phenomena) - Spectrum analysis (Fourerier, DFT, FFT) - Noise and sound standards- Math of Music- Electroacoustics- Studio equipment- Sound synthesis - Speech signals- Speaker sets
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